by The seasons are not what they used to be.
People who live in the middle latitudes of the Earth are used to spring, summer, autumn and winter. If you are in the northern hemisphere, you may have noticed plants blooming earlier than usual. It’s not your imagination: a study in 2022 showed that spring has blossomed coming a month earlier in the UK due to climate change.
For new series on the seasons and how a warming climate is tackling them, over the coming months we will be examining the consequences of these wrinkles in nature’s calendar.
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How plants sense the seasons
Other species cannot coordinate their activities around date and time. Plants, the cornerstone of most ecosystems, keep up to date by responding to changes in light and temperature, says Paul Ashton, head of biology at Edge Hill University.
Plants are among the first to know when the days start to shorten in autumn, as they use a pigment called phytochrome to detect changes in red light.
“Although this subtle change escapes humans (our eyes are not sensitive to this part of the spectrum) a plant can detect this transition and begin to change.”
“Just as autumn can engineer a drop in the level of the hormone serotonin in our blood, a plant that has sensed the approach of winter will increase the production of a hormone called abscisic acid,” says Ashton. Absoxic acid causes deciduous trees to shed their leaves and grow tough winter buds that are resistant to frost.
Temperature tells many plants when to start growing in the spring. Ashton says it’s not clear how plants sense this, but again, pigments in their cells likely play a role.
“[Plants] the days feel warmer and their spring development has changed in a way that is similar to people feeling heat on their skin and therefore stepping out with fewer layers of clothing,” he says.
Read more: Plants are blooming earlier than ever – here’s how they feel about the seasons
That’s where climate change complicates things: rising air temperatures are leading to shorter and milder winters. Since 1986, plants in the UK welcome spring 26 days earlier, on average.
This relatively rapid change has divided settlement between plants and animals over thousands of years.
“Insects used to feasting on April flowering plants may find themselves a month late if warmer temperatures mean the plants now flower in March,” say Chris Wyver and Laura Reeves, PhD candidates who study pollination and climate change at the University. of Reading.
Read more: Plants are flowering a month earlier – this could be due to pollinating insects
Out of the loop
Hungry bugs are bad enough. But if insects are emerging too late to visit eye-catching flowers, the entire ecosystem suffers.
“Take, for example, the oak woodland birds of Europe, such as the blue kite, the great hornbill and the great hornbill,” says Charlie Gardner, a lecturer in conservation biology at the University of Kent. Caterpillars are emerging earlier than before, and the birds that eat them can’t keep up.
“For every ten-day advance in caterpillar emergence, the birds can only bring forward their egg-laying by three to five days, depending on the species,” he says.
Read more: Climate change is throwing the natural world out of whack – and we should all be worried
Freaky weather, a more common feature of our warming climate, can confuse wildlife’s finely calibrated senses and trick some species into thinking the season is changing even though they weren’t paying attention.
Stuart Thompson, senior lecturer in plant biochemistry at the University of Westminster, highlights how the drought that hit Europe in 2022 has convinced some trees to lose their leaves – giving the impression of mid-autumn the month of August.
Read more: Drought: why some UK trees are losing their leaves in August
Across the broader trends documented by scientists at least one thing is consistent: winter is being pushed from both sides as the world warms.
“Almost five decades of satellite observations are now available to climate researchers,” says Jadu Dash, professor of remote sensing at the University of Southampton.
“Analysis of this data shows that spring has advanced by about 15 days, and autumn is similarly delayed.”
Read more: How climate change is affecting the seasons
But climate change won’t just lead to seasons where everything happens a month earlier or later. Some species will delay mating and spring earlier, but others will stick to their original schedule, taking their cues from day length rather than temperature.
The result will be chaos, says Gardner:
“If we have any chance of preserving the living planet and avoiding the extinction of a million species, we must do more than stop climate collapse. We also need to invest in conservation, to help wild plants and animals adapt to the changes we have already introduced. It would be bad news for all of us not to do so.”
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